Electronic components such as integrated circuits, resistors, and capacitors are mounted on printed circuit boards. With electronic components made more compact in recent years, electronic components mounted on one printed circuit board are increasing in number and kind. Due to demands for downsized electronic components, chip scale packages (CSPs) are placed on substrates.
A CSP has a main surface on which terminals are arranged in a regular array, and a solder bump is formed on each of these terminals. For a CSP to be surface mounted on a printed circuit board, the solder bumps formed on the terminals are made to land on electrodes called lands on the printed circuit board. This is followed by heating, reflowing, and cooling in this order, thereby creating an interconnection between the CSP and the printed circuit board. This enables the terminals on the CSP to be electrically connected to the lands on the printed circuit board, and to be bonded to the printed circuit board due to the solder.
When thermal stress generated by thermal cycles, or external force, is applied to a CSP that is surface mounted on a printed circuit board, the portion of the CSP bonded to the printed circuit board may lack sufficient strength if it is only due to solder. Moreover, connection only due to solder lacks sufficient strength against impact caused by dropping. Therefore, reinforcing resin is used to reinforce the solder-bonded portion of the CSP.
One method of reinforcing the solder-bonded portion by using reinforcing resin, is to allow an underfill material to enter the interstices between the main surface of the CSP with the solder bumps thereon and the printed circuit board. Moreover, Patent Literature 1 proposes a method of providing reinforcing resin on a printed circuit board in advance before placing thereon an electronic component such as a CSP, only at positions (reinforcement positions) which correspond to those on a peripheral edge portion of the electronic component. This method is much better compared to using an underfill material, in terms of facilitating repair work on electronic components.
In addition to CSPs, the following are usually mounted on printed circuit boards: electronic chip components mounted by using solder paste, such as chip resistors and chip capacitors; and components with lead-wires such as connectors. Moreover, the facility used for mounting of such electronic components on printed circuit boards, is an electronic component mounting line which comprises in the given order: a screen printing machine for printing solder paste; an adhesive dispensing machine for dispensing an adhesive for temporary bonding; an electronic component placement machine (first electronic component placement machine) for placing small electronic chip components; an electronic component placement machine (second electronic component placement machine) for placing large electronic components including CSPs, and other kinds of electronic components such as connectors; and a reflow machine for melting solder. The accomplished configuration of such an electronic component mounting line has a history of over 20 years, and is capable of performing in one continuous flow, processes which involve: placement of electronic components of sizes ranging from miniscule to large, up to 30 millimeters square; and reflow of the resultant assembly.